1. Field of the Invention
The present invention relates to a linear motion rolling guide unit suitably applied for machine tools, industrial robots, precision processing equipment and testing equipment, in which sliders slide on track rails with a number of rolling elements interposed therebetween.
2. Description of the Prior Art
Linear motion rolling guide units generally have sliders mounted astride track rails with a large number of rolling elements interposed therebetween so that the sliders can slide on the track rails. Such linear motion rolling guide units are available in a variety of types. As an example of such a linear motion rolling guide unit, a four-raceway endless linear motion rolling guide unit will be explained by referring to FIG. 1 to FIG. 4.
The four-raceway endless linear motion rolling guide unit has a track rail 1 with a substantially I-shaped cross section, a slider 2 straddling the track rail 1 in such a way that it can move relative to or slide on the track rail 1, and a number of cylindrical rolls 3 rotatably interposed between the track rail 1 and the slider 2. The track rail 1 is formed with recessed grooves 8 extending longitudinally on both sides 18 thereof, which form raceway surfaces 5, 6. The recessed grooves 8 of the track rail 1 are formed at the upper and lower edges thereof with longitudinally extending, inclined upper and lower raceway surfaces 5, 6 respectively. The slider 2 has a casing 4 which is formed with a recessed portion 10 so that the casing can straddle the track rail 1, and end caps 7 attached to both longitudinal ends of the casing 4. To seal the boundary between the track rail 1 and the slider 2 when the slider 2 slides on the track rail 1, the ends of the end caps 7 are each provided with an end seal 20 and the underside of the slider 2 with an under seal 22.
The recessed portion 10 of the casing 4 is formed with a longitudinally extending upper raceway surface 11 and a lower raceway surface 12 at locations facing the upper raceway surface 5 and the lower raceway surface 6 of the track rail 1. Between the upper raceway surface 11 and the lower raceway surface 12 of the casing 4 is formed an engagement groove 15, which receives an engagement projection 16 formed on the retainer 9. The retainer 9 has one part thereof loosely fitted in the recessed groove 8 of the track rail 1 and is fixed to the casing 4 by bolts 17.
In the above construction of the 4-raceway endless linear motion rolling guide unit, two raceways X1, X2 are formed on each side of the track rail 1, one between the upper raceway surface 5 on the track rail 1 and the upper raceway surface 11 on the casing and the other between the lower raceway surface 6 on the track rail 1 and the lower raceway surface 12 on the casing 4. Hence, a total of four raceways are formed on both sides of the track rail 1. In these roller raceways, a number of cylindrical rollers 3 roll in contact with the facing raceway surfaces 5, 11/6, 12. The casing 4 is formed with return passages 13, 14, and the end caps 7 are formed with direction changing passages 25, 26 that connect the roller raceways and the return passages 13, 14.
These direction changing passages are explained by referring to FIG. 8. The end surfaces of the end caps 7 are formed with two direction changing passages 23, 24/25, 26 on each side of the track rail 1 that cross each other without interference. Thus, as the slider 2 slides on the track rail 1, a number of cylindrical rollers 3 trapped between, for example, the facing raceway surfaces 5 and 11 are led into the direction changing passage 23 and then into the return passage 13, circulating in an endless circulation path. Likewise, a number of cylindrical rollers 3 trapped between the facing raceway surfaces 6 and 12 move into the direction changing passage 24 and into the return passage 14, circulating in an endless circulation path. The same applies to the direction changing passages 25, 26 and their explanation is omitted.
The end cap 7 is provided with an end seal 20 that seals the gap between the track rail 1 and the slider 2, and is formed with oil supply ports 27, 28 and oil grooves for feeding lubricating oil to the raceways X1, X2 between the raceway surfaces 5 and 11/6 and 12 on the track rail 1 and the slider 2. The oil supply ports 27, 28 are provided on each side of the end cap 7 so that lubricating oil can be supplied from either side.
The oil groove comprises: a first oil groove 29 that extends from the oil supply ports 27, 28 on the left and right side toward the center of the end cap 7; a second oil groove 30 that supplies lubricating oil to the raceway surfaces 5, 6 formed on the side wall surface 18 of the track rail 1; and a communicating oil groove 31 that connects the first oil groove 29 and the second oil groove 30. The communication oil groove 31 is located on the center line of the end cap 7. The lubricating oil supplied from one oil supply port 27 passes, as indicated by arrows 32, 33, 34, through the first oil groove 29 formed in the end cap 7, branches at the communicating oil groove 31 and from there flows through the second oil groove 30 to the raceways X1, X2 on the left and right side of the track rail.
Described above is the construction of the conventional 4-raceway endless linear motion rolling guide unit, with the slider 2 normally placed on a horizontal surface for sliding. That is, the first oil groove 29 and the second oil groove 30 are kept horizontal during use, as shown in FIG. 8. As application of the linear motion rolling guide unit widens, a need arises to use the linear motion rolling guide unit in a vertical position or in an inclined position.
Let us consider a case where the conventional linear motion rolling guide unit is used in an inclined attitude, for example, with the right side tilted downward in FIG. 8. When the lubricating oil is led through the first oil groove 29 into the communicating oil groove 31 and from there into the second oil groove 30, the oil is affected by gravity and flows mainly in the direction of arrow 33, with the result that the oil flow toward the direction of arrow 34 tends to be insufficient. That is, of the raceways located on the left side and right side of the track rail 1, the raceway positioned relatively higher will be supplied with a smaller amount of lubricating oil. In other words, only one side of the track rail is lubricated. Since the raceways are the portions that bear heavy loads, it is an important issue that should be addressed how to prevent the one-side lubrication or how to supply oil in equal amounts to the left and right side raceways.